Electron discharge device



Nov. 26, 1963 J. L. CARTER ETAL 3,112,426

ELECTRON DISCHARGE DEVICE Filed Dec. 5, 1961 [2 |a j 1 4 ..2o l l c l f l I I 1 I I I INVENTORS JOHN 1.. cARrEk a IRVING EINGOLD.

ATTORNEY:

United States Patent ()fiice 3,112,426 Patented Nov. 26, 1963 The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment of any royalty thereon.

The present invention relates to gaseous discharge switching devices and more particularly to an improved resonant window assembly for such switching devices.

For satisfactory operation of TR and ATR tubes, it is necessary to achieve low recovery or gas deionization time and low leakage power. Upon cessation of the trans mitter energy, the recovery or deionization process must proceed by operation of one or more of three processes; namely, attachment, recombination and diffusion. In the attachment process, water vapor is employed as an additive inasmuch as water vapor has a high electron afiinity. The fast deionization achieved, however, has resulted in an increase in the arc-loss or thermal energy dissipated within the gaseous discharge container. In many cases this thermal energy is sufliciently high to melt a dielectric material and thus shorten tube life. By using a pure, dry, noble gas such as argon, krypton or xenon, the arc-loss can readily be reduced. However, since simple difiiusion is the deionization mechanism relied upon in such devices, the recovery time is increased beyond tolerable limits. While encapsulated dielectric structures, as described in US. Patent No. 2,791,720, issued May 7, 1957 to F. A. Lesch, may be optimized for arc-loss, such a structure still presents a relative long diffusion path. The addition of water vapor presents certain disadvantages in that oxidization of any exposed metallic surfaces is likely to occur and temperature extremes will result in drastic changes in water vapor pressure thereby altering the gaseous atmospheric composition.

It is an object of the present invention to provide an encapsulated resonant window assembly having improved electrical characteristics of low arc-loss and short recovery time.

It is another object of the present invention to provide an improved encapsulated resonant window assembly wherein the diffusion path is reduced to approximately equal the mean free path of a selected pure, noble gas contained therein.

In accordance with the text Basic Data of Plasma Physics by Sanborn C. Brown, Technology Press and John Wiley & Sons, Inc., New York, 1958, pages 48-50, the diffusion length or gap dimension is defined by where A characteristic diffusion path D=diffusion coefiicient of gas, and T =recovery time.

For parallel plate geometry the diffusion length is defined by tilifil From Equation 2, it can be seen that as the spacing is decreased the dilfusion length A decreases. It can also be shown that which shows that as the distance L becomes smaller, the recovery time awill also become shorter.

In accordance with pages 2 and 3 of the aforementioned text, the mean free path I of a selected gas may be defined as 1 o wherein:

P is the collision probability that occurs when an electron travels 1 cm. at a pressure of 1 mm. at 0 C.; and

Where p is the actual pressure employed; and T is the electron temperature during ionization.

In accordance with the present invention, a relatively short diffusion path approximating the mean free path of a selected pure, noble gas is provided in a resonant window assembly having an integral gaseous atmosphere contained within an encapsulated dielectric structure.

For a better understanding of the invention, together with other and further objects thereof, reference is made to the following description taken in connection with the accompanying drawing in which:

FIGURE 1 is a perspective view of the present invention with part of the encapsulated structure broken away and shown in section for clarity; and

FIGURE 2 is a front elevation of the encapsulated structure and shows the relative position of the indented portion and the dielectric window.

Referring now to the drawing, at 10 there is shown an encapsulated window assembly in accordance with the invention. A metal plate 1 2 is provided with a resonant iris covered with a dielectric enclosure 14 of conventional construction. The inner portion of plate 12 is heavily glazed in the area indicated at 16 with a beaded, powdered glass suspension. A trough 18, formed from glass tubing and provided with a central indented portion 20 longer than the resonant dielectric enclosure 14, is heat sealed to the glass inside portion of plate 12. With such an arrangement, the trough 18 comprises two substantially bulbous or arcuate portions 22 and 24 having proximate walls formed by the indented portion 20. Looking at trough 18' from the plate 12 of encapsulated window 10, the surfaces of the bulbous or arcuate portions 22 and 24 are concave in cross sect-ion land the end surface of the indented portion 20 opposite dielectric enclosure 1-4 is substantially flat. If desired, the flat surface of indented portion 20 may be made as wide as the resonant iris covered by dielectric enclosure 14. As shown, the flat surface of indented portion 20 opposite dielectric enclosure 14 is spaced slightly therefrom substantially parallel to dielectric enclosure 14 and extends beyond the longitudinal dimension thereo. Trough 18 is provided with an exhaust stem 26 through which the completed encapsulated assembly may be evacuated and sealed with the desired gaseous atmosphere. For use at microwave frequencies, the spacing between the flat surface of the indented portion 20 and dielectric enclosure 14 corresponds ltO dimension L in Equation 3 and, for optimum results, this spacing may generally be between 0.010 and 0.050 inch. This will permit proper relationship between diffusion length and mean free path to provide fast recovery time with pure, noble gas fills such as argon, and without the use of quenching agents such as water vapor.

While there has been described what is at present considered to be the preferred embodiment of this invention, it will be obvious to those skilled inthe art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

l. A gas filled encapsulated window assembly comprising, a metallic plate having a resonant iris therein, a dielectric enclosure covering said resonant iris, a trough made from glass tubing and comprising two interconnected bulbous portions extending along the longitudinal dimension of said plate, the interconnecting portion having .a .fiat surface opposite said dielectric enclosure and 4 proximately spaced therefrom, the remainder of said trough being hermetically sealed to said plate.

2. A gas filled encapsulated window assembly comprising, a metallic plate having a resonant iris therein, a dielectric enclosure covering said resonant iris, a trough made from glass tubing and sealed to said plate and including two parallel spaced containers coextensive with the longitudinal dimension of said plate and on opposite sides of said iris, the proximal ends of said containers being connected by a fiat surface proximate said dielectric enclosure.

3. The gas filled encapsulated window in accordance with claim 2 wherein the width of said flat surface is substantially the width of said iris.

References Cited in the file of this patent UNITED STATES PATENTS 2,957,148 Alexander Oct. 18, 196Q 

1. A GAS FILLED ENCAPSULATED WINDOW ASSEMBLY COMPRISING, A METALLIC PLATE HAVING A RESONANT IRIS THEREIN, A DIELECTRIC ENCLOSURE COVERING SAID RESONANT IRIS, A TROUGH MADE FROM GLASS TUBING AND COMPRISING TWO INTERCONNECTED BULBOUS PORTIONS EXTENDING ALONG THE LONGITUDINAL DIMENSION OF SAID PLATE, THE INTERCONNECTING PORTION HAVING A FLAT SURFACE OPPOSITE SAID DIELECTRIC ENCLOSURE AND PROXIMATELY SPACED THEREFROM, THE REMAINDER OF SAID TROUGH BEING HERMETICALLY SEALED TO SAID PLATE. 